In a conversation with a customer a few minutes ago, he mentioned that his primary fermentation fridge's controller went bad on him after four years. It seems that it lost its "charge." He said that it looked like something had eaten at the bulb to the point that a hole developed in it letting the gas get out. His theory was that the moisture and CO2 in the enclosed space formed carbonic acid or something and eat a hole. Anybody else ever hear of this sort of thing. We have one in a fridge that we store yeast in for about 7 years and it appears fine.

I just got one and noticed that it changed color in a couple weeks from touching the aluminum interior walls of the freezer. Galvanic corrosion with the copper probe. I could certainly imagine it eating a hole over time if it continued.Be wary of strong drink. It can make you shoot at tax collectors -- and miss. ~~Robert A. Heinlein: The Notebooks of Lazarus Long

I've noticed a bit of corrosion on my Johnson controller's sensor after many years of use. It developed the most when I used to leave it immersed in a bottle of water to curtail compressor cycling. Now, I just secure it on the outside of the fermenter with the giant o-ring seal from a discarded 5-gallon bucked lid. I don't want to watch it slowly erode away. How about smearing some protective silicone-based grease on it? I've also thought about dipping it in that liquid rubber substance sold at auto parts stores for tool handles. Any other ideas?